In a turning machine, when a blade of a tool is chipped during workpiece processing, torque of a motor moving the tool or torque of a main axis motor moving a workpiece varies. A processing load monitoring method disclosed in PTL 1 detects chipping of the blade of the tool on the basis of the torque change. That is, in the processing load monitoring method disclosed in PTL 1, an actual torque change is compared with a threshold value for abnormality determination, and when the actual torque exceeds the threshold value, it is determined that the chipping occurs.